1. Field of the Invention
Embodiments of the present invention generally relate to a method of depositing a gate hard mask for a gate structure and computer readable programs executable to perform the method.
2. Description of the Related Art
When forming a gate structure, a gate oxide layer 2 is deposited on a substrate 1 followed by a polysilicon gate layer 3. FIG. 1A shows an exemplary prior art gate structure 5 before any etching. The polysilicon gate layer 3 and the gate oxide layer 2 need to be etched, so a gate hard mask 4 is formed over the polysilicon gate layer 3. The gate hard mask 4 is formed by plasma enhanced chemical vapor deposition (PECVD). The polysilicon gate layer 3 and gate oxide layer 2 are then plasma etched (i.e. dry etched). Next, the remaining gate hard mask 4 must be removed. A good removal process is to use an etching solution (i.e. wet etch). Unfortunately, while the wet etch is good at removing the gate hard mask 4 layer, it is also good at removing the gate oxide layer 2. As can be seen from FIG. 1B, the wet etch removes the gate hard mask 4, but it also creates an undesirable undercut 8 in the gate oxide layer 2. The wet etch removal ratio (WERR), which is defined as the wet etch removal rate of one material divided by the wet etch removal rate of another material, for a PECVD gate hard mask 4 relative to the gate oxide 2 is typically 3 to 4.
Accordingly, there is a need in the art to provide a gate hard mask effective for dry etching the polysilicon gate layer and gate oxide layer and also have a high WERR to prevent undesirable undercutting of the gate oxide layer.